Generally a toothbrush has a head and a handle disposed along a longitudinal axis, the head having bristles arranged in tufts extending from a face thereof ("the bristle face") in a general bristle direction. It is known, e.g. in British Standards Institution publication BS 5757:1979 "Specification for Toothbrushes" that the stiffness of a toothbrush bristle is related to its length and diameter. For bristles of the same diameter and material, longer bristles will be less stiff than shorter bristles.
Generally the bristle face is planar. Toothbrushes are disclosed in GB 501124 and GB 1098933 in which the ends of the bristles remote from the bristle face (the "remote ends") generally lie in a non-planar surface, those of GB 501124 lying in a stepped surface, those of GB 1098933 lying in an undulating surface. To maintain a uniform stiffness of the bristles of these latter toothbrushes, the bristle face is displaced from planarity in the general bristle direction in a manner which corresponds substantially to the surface in which the ends of the bristles lie. In U.S. Pat. No. 4,010,509 a toothbrush with parts of its bristle face displaced from planarity is disclosed, again to cause the bristle ends to lie in a corresponding non-planar surface. U.S. Pat. No. 4,776,054 discloses a toothbrush in which parts of the bristle face are displaced from planarity in the general bristle direction, but in which the bristles are all of substantially the same length, the displaced parts being used to impart a tilt to the tufts. EP 0175084A, U.S. Pat. No. 4,010,509 and U.S. Pat. No. 5,325,560 disclose toothbrushes in which the bristle face has an undulating profile widthways. U.S. Pat. No. 4,852,202 discloses a toothbrush with a raised "working platform" from which extend short sloping bristles. JP 04-122306A discloses a toothbrush with a longitudinally aligned ridge with a corresponding bristle profile. EP 0471312 A discloses a toothbrush in which the bristle surface is in a stepwise shape, with longer bristles on the lower steps.
It can be desirable to vary the stiffness of the bristles of toothbrushes along the length of the head of the toothbrush, for example so that the toothbrush may have stiff bristles to clean in the interdental spaces, and softer bristles to clean the broad areas of the teeth, or vice versa. This variation in stiffness can be achieved by the use of different bristle fibre materials, diameters, packing density etc. but such approaches can lead to manufacturing complexities.
The object of the present invention is to provide a relatively simple construction of toothbrush which enables the stiffness of the bristles to be varied along the length or across the width of the head of the toothbrush.